426 On Geometrical Proportion. 



with that of 2, then we have C6-B8 + A2= 10 = 4. 

 The body therefore condenses with the force of 4. Thus 

 then, by numerical expression, we find the conversion of 

 liquids into gases, and vice versa; and hence this conversion 

 depends more or less on atmospheric pressure. 



Although the force of pressure is too slight to affect solids, 

 yet crystallization is in a certain degree dependent on it ; the 

 cohesive power in the liquid would not be sufficient of itself. 



Hence, though the points of condensation and evapora- 

 tion are established at certain standards, it is merely because 

 the pressure is similarly established at a certain standard 

 point (30 inches). The boiling point of water at this pres- 

 sure is 212°. On the tops of mountains a much less degree 

 of heat will suffice*, and in an exhausted receiver it will 

 boil at 70\ 



On the contrary, when the pressure is increased (in pits 

 or mines), a greater heat is of course required, and by arti- 

 ficial pressure water may almost sustain any heat without 

 evaporating f. The exact ratio of the decrease of heat for 

 the decrease of pressure, or the increase of heat for the in- 

 crease of pressure, in the process of ebullition in water or 

 other fluids, has not, I believe, been hitherto determined. 



Thos. Charlton Speer. 



May 19, 1809. 



LXXV. On Geometrical Proportion. By Wm. Marrat, 

 Esq., of Boston, Lincolnshire. 



To Mr. Tilloch, — Sir, 

 JL he doctrine of proportion is well known to be of so much 

 importance to mankind in general, that any attempt to elu- 

 cidate its principles cannot be deemed entirely useless. A 

 great part of the obscurity with which this subject is enve- 

 loped, arises from the vague and ambiguous manner in 



* See Saussure, on the Alps, Sec 



+ Hence, bv means of an instrument that would very sensibly measure the 

 degrees of heat, we might (ceteris paribus) ascertain heights in the atmo- 

 sphere, and our distance above it, by the decrease of the boiling point ; and, on 

 the other hand, Our distance below it (in pits for instance) by its increase. 



which 



